1. Field of the Invention
The present invention relates to a fluid pressure cylinder, such as, an air cylinder, or an oil hydraulic cylinder, and particularly to a pressure-intensifying type fluid pressure cylinder in which the application of force is intensified around the end of movement of a piston rod.
2. Description of the Prior Art
A fluid pressure cylinder is used in various types of operation mechanisms, such as, a clamp mechanism, a compression mechanism, and a caulking mechanism. In the clamp mechanism, the compression mechanism, and the like, normally, great application force is not necessary at the beginning of the application but great application force is necessary at the end of the application. Accordingly, a fluid pressure cylinder which drives the mechanism should supply greater application force at the end of movement of a piston rod compared with that at the beginning position or at an intermediate position of such piston rods.
Therefore, when the size of (a cylinder tube of) a fluid pressure cylinder for a clamp mechanism, and the like, is designed, a fluid pressure cylinder is normally selected in which cylinder necessary application force at the end portion of application can be obtained. There is a problem that, in a case where a small size of a fluid pressure cylinder (the diameter of a cylinder tube of which cylinder is small) is sufficient with regard movement from the period from the beginning of movement of the piston rod to just before the end portion, due to the great application force required at the end of piston movement, a fluid pressure cylinder which is big, heavy, and expensive must be used.
Because of this, conventionally, a fluid pressure cylinder is provided with a booster apparatus which is connected with a pipe line supplying fluid pressure to the fluid pressure cylinder for increasing application force just before the end of piston rod movement by applying higher pressure at the end position of movement of a piston rod.
However, this kind of a booster apparatus has a problem that, not only its structure is complicated but, also, it requires at least four solenoid operated valves, which leads to increased cost.